1. Field of the Invention
This invention relates to planetary gearing, clutches and brakes of an automatic transmission for a motor vehicle. More particularly, the invention pertains to a technique for controlling operation of the clutches and brakes to produce multiple gear ratios.
2. Description of the Prior Art
This invention comprises improvements in a four speed ratio power transmission mechanism of the kind described in U.S. Pat. Nos. 4,509,389; 4,368,649, and U.S. Ser. No. 07/722,453 filed Jun. 27, 1991. These patents and application are assigned to the assignee of this invention.
U.S. Pat. No. 4,509,389 discloses a hydrokinetic torque converter located on the axis of the crankshaft of an internal combustion engine and two simple planetary gear units mounted for rotation about the axis of a driven shaft, which extends parallel to the crankshaft axis and concentrically through the gearing. The torque output element of the torque converter, which is the turbine shaft of the bladed turbine, is connected driveably to the gearing by to a drive sprocket and a chain. Clutches and brakes are used to establish and disestablish four forward driving ratios as well as a reverse drive ratio.
A first overrunning coupling and a first friction clutch are used to establish a driving connection between an input sun gear of the gearing and the driven sprocket. A second overrunning coupling and a second friction clutch located in series relationship connect the sun gear to the driven sprocket. The first friction clutch and the second friction clutch each are provided with fluid pressure operated servos that comprise an annular cylinder and a cooperating annular piston, which define pressure chambers that rotate about the axis of the gearing. When the chambers are pressurized, the pistons engage friction discs to establish a driving connection between the outer race of the companion overrunning coupling and the common rotary portions of the clutch cylinders.
U.S. Pat. No. 3,054,488 describes an overrunning coupling that is engaged and released selectively to accommodate free-wheeling in either direction and to prevent relative rotation between the coupling races in one direction. Rollers are urged into clutching engagement with inner and outer races or into a clutch release position by fluid pressure.